This invention relates to a cylinder liner of a hypereutectic aluminum/silicon alloy for use into a reciprocating piston engine and a process for producing such a cylinder liner. More particularly, this invention relates to embodiments of a cylinder liner of a hypereutectic aluminum/silicon alloy for casting into a reciprocating piston engine, and processes for producing such a cylinder liner.
Hagiwara EP 367,229 A1 discloses a cylinder liner which is produced from metal powder, such as aluminum oxide, with from 0.5 to 3% graphite particles mixed-in, which have a particle diameter of at most 10 .mu.m or less (measured in a plane perpendicular to the cylinder axis) and from 3 to 5% hard material particles without sharp edges, which have a particle diameter of at most 30 .mu.m and on an average 10 .mu.m or less. The metal powder is produced first, without mixing-in the nonmetallic particles, by air atomization of a supereutectic (the terms "hypereutectic" and "supereutectic" are used interchangeably herein) aluminum/silicon alloy having the following composition, with the remainder being aluminum (figures are in % weight based on the total metal content of the alloy, i.e. without the particles of hard material and graphite):
Silicon 16 to 18%, Iron 4 to 6%, Copper 2 to 4%, Magnesium 0.5 to 2% and Manganese 0.1 to 0.8%.
The metal powder is mixed with non-metallic particles and this powder mixture is pressed at about 2,000 bar to give a preferably tubular body. This powder metallurgically produced blank is inserted into a soft-aluminum tube, aluminum tube of corresponding shape to make a double layer tube, which is jointly sintered and shaped in an extrusion process, preferably at elevated temperatures, to give a tubular blank from which the individual cylinder liners can be produced. The embedded particles of hard material are intended to give the cylinder liner good wear resistance, while the graphite particles serve as a dry lubricant. However, to avoid oxidation of the graphite particles, the hot extrusion should take place in the absence of oxygen. There is also the danger of the graphite reacting with the silicon at high processing temperatures and forming hard SiC on the surface, which interferes with the dry-lubricating properties of the embedded graphite particles. Furthermore, local surface fluctuations in the concentration of particles of hard material and/or graphite can never be entirely eliminated.
Due to the embedded hard material particles, the hot-pressing mould wears out relatively rapidly, since the hard material particles still have, in spite of their rounded edges, a powerfully abrasive action; with reasonable effort, it is in any case possible only to round the edges partially on the particles formed by crushing comminution. The subsequent mechanical treatment of the running surface of the cylinder liner also entails high tool wear and thus high tool costs. The hard material particles exposed in the running surface have sharp edged boundaries after the surface machining and subject the piston skirt and the piston rings to relatively extensive wear, so that these must be produced from a wear-resistant material and/or must be provided with an appropriately wear-resistant coating. The known cylinder liner altogether is not only relatively expensive due to the starting materials with several separate components, but the high tool costs in connection with the plastic and metal-removing machining greatly increase the cost per piece. Apart from this, the type of manufacture of the known cylinder liner from a heterogeneous powder mixture involves the risk of inhomogeneities which, under some circumstances, cause a functional impairment, that is to say rejects, but in any case require expensive quality monitoring. Furthermore, it presupposes piston designs which are complex in engine operation and which altogether make the reciprocating piston engine more expensive.
Other disadvantages of Hagiwara, et al. '229, are due to the fact that the embedded particles of hard material, despite their rounded edges, still have strong abrasive action, thereby causing the hot pressing die to wear out relatively quickly. In any case, only a partial rounding of the particle edges formed by crushing can be achieved with justifiable effort. High tool wear, and thus high tool costs, is also associated with the subsequent machining of the surface of the cylinder liner. After machining, the hard material particles exposed on the surface, have sharp edges and cause relatively high wear of the piston and the piston rings, therefore, these have to be made of wear-resistant material or be provided with appropriate wear resistant coating.
Basically, the Hagiwara, et al. '229 cylinder liner is not only relatively expensive because the starting materials require several separate components, but also because of the high tool costs associated with the process. Additionally, because these known cylinder liners are produced from a heterogeneous powder mixture, the danger of inhomogeneities exists, which may result in impaired function, and thus in rejects, requiring careful quality control. In addition, for use in an engine, complicated piston construction is required, which makes the entire reciprocating piston engine more expensive.
Kiyota, et al., U.S. Pat. No. 4,938,810, likewise discloses a powder-metallurgically produced cylinder liner. In this patent, a large number of alloy examples are listed, and measurement data and operating data of the cylinder liners produced with these are also given. The silicon content of the examples provided are in the range of from 10 to 30%, which extends into the subeutectic region, and preferably from 17.2 to 23.6%. At least one of the metals, nickel, iron or manganese, should be present in the alloy, in an amount of at least 5% or, in the case of iron in an amount of at least 3%.
An example of an alloy composition of Kiyota, et al. '810 in % by weight, where the remainder is aluminum, and the content of zinc and manganese are not specified, and are therefore assumed to be present in trace quantities only, follows:
 Silicon 22.8%, Copper 3.1%, Magnesium 1.3%, Iron 0.5% and Nickel 8.0%.
the remainder being aluminum.
The nickel content in the alloy example given is very high. A blank for a cylinder liner is hot-extruded from the powder mixture.
Perrot, et al., U.S. Pat. No. 4,155,756, deals with the same topic. In this case, inter alia, the following composition of a powder-metallurgically produced cylinder liner is given as one example of several:
 Silicon 25%, Copper 4.3%, Magnesium 0.65% and Iron 0.8%.
the remainder being aluminum.